This invention relates to a semiconductor device and also to a method for making the same. More particularly, the invention relates to a semiconductor device which is very thin, is unlikely to break by bending stress, and is suitable for use as various types of cards, and also to a method for making such a thin semiconductor device stably and at low costs.
The formation of various types of cards such as IC cards has been proposed by utilizing a very thin semiconductor device. Hitherto, it has been difficult to obtain such cards which can stand use in practical applications owing to the is ease in breakage by bending stress.
Conventional assembling technologies of thin semiconductor devices are described, for example, in xe2x80x9cLSI Handbookxe2x80x9d (edited by the Electronic Communication Society and published by Ohom Corporation on Nov. 30, 1984, pp. 406-416). In these conventional semiconductor device assembling technologies, there have been employed semiconductor wafers which have such a thickness of approximately 200 xcexcm or over that they are very unlikely to break when direct handling is done.
As is well known in the art, a polishing method has been in wide use for thinning a semiconductor wafer. In order to uniformly process a semiconductor wafer, for example, with a process accuracy of 5% according to the polishing method, it is essential that the semiconductor wafer be set parallel to a polishing device at high accuracy and high reproducibility. For realizing such a very high level of parallel setting, a very expensive apparatus is necessary, thus having involved a difficulty in practical applications.
An attempt has been made to effect a polishing method while monitoring the thickness of a semiconductor wafer. If a region with a large area is polished according to this method, it takes a very long time, resulting in the lowering of productivity.
Alternatively, when a semiconductor wafer is polished to a very small thickness, for example, of approximately 0.1 xcexcm, there arises the problem that various types of semiconductor devices, such as transistors, formed on the surface of the semiconductor wafer are broken owing to the stress caused by the polishing.
Moreover, when such a thinned semiconductor chip is directly handled according to the prior art technologies, a problem is involved in that the semiconductor chip is broken. Thus, it has been difficult to form a semiconductor device in high yield at low costs.
Accordingly, an object of the invention is to provide a semiconductor device which can solve the problems of the prior art technologies, is unlikely to break owing to the bending stress exerted thereon, and can be utilized as various types of cards.
Another object of the invention is to provide a method for making a semiconductor device which is able to thin a semiconductor chip to a level of approximately 0.1 to 110 xcexcm and wherein such a very thin chip can be handled without involving any cracking occasion.
In order to achieve the above objects, there is provided a semiconductor device which comprises a thin semiconductor chip and a substrate which are faced to each other via an organic adhesive layer containing a multitude of conductive particles therein, a pad made of a conductive film and formed on the surface at the substrate side of the semiconductor chip, and a substrate electrode provided on the surface at the chip side of the substrate such that the pad and the substrate electrode are electrically connected to each other via the conductive particles.
The thin semiconductor chip and the substrate made of an elastic material, which are arranged in face-to-face relation with each other, are bonded and fixed together through the organic adhesive layer, so that when exerted with a bending stress from outside, they are very unlikely to break.
The electric connection between the semiconductor chip and the substrate is ensured by means of the conductive particles present in the organic adhesive. The conductive particles are deformed by application of a pressure to the pad of the semiconductor chip and the electrode of the substrate which are arranged in face-to-face relation with each other. The thus deformed conductive particles serve to electrically connect the semiconductor chip and the substrate with each other, and thus, the electric connection between the pad and the electrode is very reliable.
A passivation film having a given pattern is formed on the semiconductor chip, and the pad is formed on a portion where no passivation film has been formed. The thickness of the pad is smaller than that of the passivation film, so that the conductive particles present between the pad and the electrode being faced to each other are effectively suppressed from migration to outside. In this way, the pad and the electrode can be reliably, electrically connected by means of the conductive particles.
A method for making a semiconductor device for the purpose of achieving the another object of the invention comprises bringing a semiconductor wafer, which has been attached to a tape, into contact with an etchant while rotating the wafer within an in-plane direction thereof or laterally reciprocating the wafer at a high speed so that the semiconductor wafer is uniformly reduced in thickness by etching, dicing the thus reduced semiconductor wafer for division into a plurality of chips, and subjecting individual thin chips to hot-pressing against a substrate to bond them on the substrate one by one.
While rotating the wafer in an in-plane direction thereof or laterally reciprocating it at a high speed, the semiconductor wafer is brought into contact with an etchant, so that the wafer is very uniformly etched. Thus, there can be obtained a very thin semiconductor wafer (0.1 to 110 xcexcm) which is substantially free of any irregularities and distortion.
A plurality of the thin semiconductor chips which are obtained by dividing the very thin semiconductor wafer into smaller-sized chips are, respectively, separated from the tape which is a first substrate, and are heated on a second substrate and welded by compression pressure. Thus, irrespective of the semiconductor chips being very thin, the chips can be fixedly adhered or bonded on the second substrate without involving any undesirable cracking occasion. Especially, when a non-rigid tape is used as the first substrate, only a desired chip is pushed upwardly and is selectively heated, so that it is very easy to adhere the desired chip on the second substrate. For the division of the wafer into the chips, it is preferred from the standpoint of practical applications that the wafer is completely separated into individual chips by dicing.
The adhesion between the second substrate and the semiconductor chip is effected through a conductive adhesive, by which any wire bonding becomes unnecessary, thus being very effective in the simplification of the steps and the reduction of costs.